Dr. Madeline Meier Responds to Latest IQ and Marijuana Studies

Today, Dr. Madeline Meier, Professor at Arizona State University, commented on two studies (here and here ) regarding IQ and marijuana use. Dr. Meier stands firm by her previous research showing an up to 8-point reduction in IQ among heavy marijuana users. Her statement is here:

“Unfortunately for your headline writers, there is no controversy here. Our 2012 study (Meier et al. PNAS 2012) reported cognitive decline among individuals with a far more serious and far more long-term level of cannabis use. That is, we found cognitive decline in individuals followed up to age 38 who started cannabis use as a teen and who thereafter remained dependent on cannabis for many years as an adult. This new study is different; the two papers report about completely different doses of cannabis, and about participants 2 decades apart in age. The new study reports cognitive test scores for individuals followed up to only age 17-20, fewer than half of whom had used cannabis more than 30 times, and only a fifth of whom used cannabis daily for > 6 months. This new study and our prior study agree and both report the same finding: no cognitive decline in short-term low-level cannabis users. The message from both studies is that short-term, low-level cannabis use is probably safer than very long-term heavy cannabis use. The big problem remains that for some teens, short-term low-level teenaged cannabis use leads onward to long-term dependence on cannabis when they become adults. That is what is cause for concern.”

“Imagine if a study reported that teenagers drinking alcohol didn’t harm cognitive function by age 17-20, would you reasonably conclude from that study that persistent alcoholism for years cannot damage the cognitive function of adults in their late thirties? Hardly.”

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